Method and equipment for intercepting telephone calls

ABSTRACT

The invention concerns a method of intercepting a telephone call in a telecommunications system using at least one switch ( 12, 13; 24 ), in which signals in an interception loop ( 16 ) in said switch ( 12; 24 ) and to which the pulse coded multiplex (PCM) containing the call to be intercepted has been diverted are sampled at high impedance before they are directed to the addressee ( 14 ). The signal sampled at high impedance is directed to interception equipment ( 110 ) which extracts said call to be intercepted from the PCM. The signals in said interception loop ( 16 ) can include voice data and signaling interception data or only voice data, interception data concerning said call to be intercepted being transmitted to said interception equipment over a dedicated line ( 112 ).

BACKGROUND OF THE INVENTION

The field of the invention is that of telecommunications. To be moreprecise, the invention concerns lawful telephone tapping systems, alsoknown as call interception systems.

Telephone call interception systems have been used for many years inlawful telephone tapping systems (i.e. systems under the control of adefined authority, conventionally the state).

The oldest technique consists in applying a physical tap to the cablesof a subscriber under surveillance. Unfortunately, this technique isimpractical and easily detectable. Moreover, it is not compatible withdigital communications (Integrated Services Digital Network—ISDN) orwith mobile telephone systems.

Another technique consists in analyzing everything on a given line andthen extracting therefrom the pertinent information. Clearly thissolution is costly and complex, and ill-suited to universal telephonetapping, regardless of the communications system used.

A further technique that has been used is to create a conference callbridge within the exchange to which the subscriber to be intercepted isconnected. The problem with this technique is that defects due to thevarious parties involved in the conference call bridge, and inparticular the interceptor, are additive. It is therefore relativelyeasy to detect. Moreover, it is not possible to effect more than oneinterception of the same subscriber using this technique.

However, it is desirable for this to be possible in some situations.This is the case in particular when the same communications systemcovers geographical areas administered by different authorities. Forexample, a mobile radio system satellite can conventionally cover aplurality of states, each of which has its own law and its ownrequirements in terms of lawful telephone tapping. Consequently, varioustelephone tapping control centers must be provided (one per area). Itmust of course be possible for more than one of these centers tointercept the same subscriber, if necessary.

Generally speaking, the various systems that have been used in the pasthave at least some of the following drawbacks:

they are easily detectable by a subscriber,

they necessitate a great amount of processing to extract the wantedinformation from the signals intercepted,

they cannot be used interchangeably on all types of network (analogtelephone network, digital network, cellular mobile radio network,satellite communication network, etc.),

they do not provide for selective interception as a function ofdifferent centers associated with separate geographical areas,

they are not completely effective against call rerouting and subscribernumber changing techniques,

they cannot transmit intercepted data to more than one separate controlcenter,

etc.

One objective of the invention is to overcome these various drawbacks ofthe prior art.

To be more precise, a first objective of the invention is to provide amethod of intercepting calls sent and/or received by a subscriber,regardless of the communications systems employed, even if thesubscriber uses particular means such as call rerouting, call transfer,number change, etc.

Another objective of the invention is to provide a method of the abovekind which can intercept all types of call (voice, fax, data) and allrequired signaling information.

A further objective of the invention is to provide a method of the abovekind which necessitates simple and effective processing of the data tobe intercepted and which is totally undetectable by subscribers.

A further objective of the invention is to provide a method of the abovekind providing for selective telephone tapping in different geographicalareas and for transmitting an intercepted call to a plurality ofinterception control centers, corresponding to different beneficiaries(the courts, the police, etc.), for example.

A further objective of the invention is to provide a method of the abovekind which provides for selective tapping of a group of lines(corresponding to all the lines used for an exhibition or all the linesof a company, for example).

The above objectives, and others that emerge more clearly hereinafter,are achieved by the invention by means of a method of intercepting atelephone call in a telecommunications system using at least one switch,in which method signals in an interception loop in said switch and towhich the pulse coded multiplex (PCM) containing the call to beintercepted has been diverted are sampled at high impedance before theyare directed to the addressee.

SUMMARY OF THE INVENTION

This makes it possible to perform lawful telephone tapping without thisbeing detectable by the users. There is no restriction on thecommunications systems used (in particular digital and mobiles systems).

The signal sampled at high impedance is advantageously directed tointerception equipment which extracts said call to be intercepted fromthe PCM. The interception equipment can be inside the switch or at aseparate location.

In a first embodiment of the invention, the signals in said interceptionloop comprise voice data and signaling interception data. In this case,the interception equipment first extracts the interception data from thesampled signal and then performs the interception proper.

In a second embodiment, offering enhanced security, the signals in saidinterception loop comprise only voice data, interception data concerningsaid call to be intercepted being transmitted to said interception uniton a dedicated line by control means of the switch handling said call tobe intercepted.

In this case, knowing only the content of the sampled signal is notsufficient to perform the interception.

In a third embodiment, part of the interception data from a call istransmitted together with the signals conveyed by said interceptionloop, and part via a dedicated line.

Said interception equipment is advantageously connected to aninterception control center which in turn feeds one or more separatetelephone tapping centers. In the invention, there is no intrinsiclimitation on the number of telephone tapping centers it can feed.

Each of said telephone tapping centers preferably corresponds to ageographical interception area, such as a state or an administrativeregion. More than one telephone tapping center can of course beallocated to the same geographical area.

Each of said geographical interception areas is defined by at least oneof the following, for example:

a list of identifiers of cells of a cellular network forming saidgeographical interception area,

a list of dialing prefixes allocated to said geographical interceptionarea,

at least one item of information, supplied by way of a signalingparameter, defining the geographical interception area to which the callto be intercepted relates, and

at least one item of information, supplied by the switch, defining thegeographical interception area to which the call to be interceptedrelates.

This assures great flexibility, the invention requiring no correlationbetween the geographical interception areas and the coverage areas ofthe switch.

An advantageous feature of the invention is that said interception cancover a plurality of lines corresponding to the same source and/or thesame destination (for example an exhibition, a company, etc.).

Said telecommunications system can be one of the following:

an integrated services digital communication network,

a cellular mobile radio network, or

a satellite radio network.

The invention also concerns the interception equipment used in a methodas described hereinabove.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the invention will become more clearlyapparent on reading the following description of a preferred embodimentof the invention and from the accompanying drawings, in which:

FIG. 1 shows the general principle of the interception method of theinvention, and

FIG. 2 shows the complete architecture of a system according to FIG. 1suitable for use with the Globalstar system.

DETAILED DESCRIPTION OF THE INVENTION

1—Glossary

To simplify the following description and the figures, the mainabbreviations employed and their usual meaning are listed below:

BSS base station; IA interception area; IE interception equipment; IMCinterception management center; IRI interception related information; LElocal exchange; LEA lawful enforcement agency; LEMF lawful enforcementmonitoring facilities; MSC mobile switching center; MSISDN internationalmobile station ISDN number; PCM pulse coded multiplex; RCP radio controlpoint; SSP service switching point.

2—General Principle of the Invention

FIG. 1 shows the general principle of the invention. As indicated above,the objective of the invention is to intercept telephone calls sentand/or received by a target telephone terminal 11.

The target telephone terminal can be of any type (analog, digital,fixed, portable, etc.). It can also correspond to a set of identifiedterminals (corresponding to a set of lines of a company or the linesused for an exhibition, for example).

The target terminal 11 is conventionally connected to a telephonenetwork via a local exchange (LE) 12, in turn connected via thetelephone network to the local exchange 13 from which the terminal 14 ofthe other party to the call depends.

According to the invention, the pulse coded multiplex (PCM) 15 carryingthe call in the exchange 12 is diverted to a dedicated PCM loop 16before it is passed in the conventional way to the remote exchange 13.There is a high-impedance sampling point 18 on the PCM loop 16. Thesignal sampled at the high impedance is transmitted (at 17) tointerception equipment (IE) 110, which can direct the intercepted callsto one or more interception management centers (IMC) 111 ₁ through 111₃.

Interception therefore occurs at a time when the voice signal is easilydecodable. The interception is undetectable and in particularimperceptible to the subscriber.

Two options are available:

either the signaling interception data and the voice signal are sampledon the PCM loop 16,

or only the voice signal is sampled, on the basis of signalinginterception information transmitted over a separate line 112 (whichdelivers the interception information PS and CIC, for example).

Note that the PCM loop 16 can be local (inside the exchange 12) or atany appropriate remote location. The same applies to the IE 110.

Although only one loop 16 is shown, a plurality of similar loops couldobviously be provided in an exchange.

3—Example: the Globalstar System

One particular embodiment of the invention suited to the Globalstarnetwork is described below. In the context of this network, the sameinterception management center (IMC) may need to manage a plurality ofdifferent geographical interception areas (IA). The coverage of a singlesatellite may correspond to more than one state, each of which can haveits own rules and requirements for lawful telephone tapping.

FIG. 2 shows the general architecture of the system employed.

The target mobile terminal 21 is linked to a base station (BSS) 22 via asatellite 23. The DSS 22 is connected to a service switching point (SSP)25 which is part of a mobile switching center (MSC) 24. The PCMcontaining the call to be intercepted transits via the interception PCMloop 16 in the SSP 25 and is then directed to the remote exchange 13 towhich the remote terminal 14 is connected.

The interception system of the invention is therefore based on the useof interception equipment (IE) 110 added to the SSP and an interceptionmanagement center (IMC) 26. The functions it offers include real timemonitoring of call traffic in one or more geographical interceptionareas (IA) for particular subscribers.

The system can intercept the following information:

information carried by the voice channel (voice, fax, data),

interception related information (IRI), including in particular:

some of the use information,

the content of short messages,

additional data such as the date and time of the events concerned andthe location of the mobile station.

Because interception is effected at high impedance on the PCM loop 16,it is not detectable by the parties to the intercepted call and has noeffect on any subscriber services.

One or more interception equipment units 110 _(l) through 110 _(n) canbe associated with each SSP 25. An interception management center 26 cansupervise one or more MSC 24.

According to the invention, the IMC 26 can manage more than onegeographical interception area (IA). An IA is a subset of thegeographical coverage area associated with a satellite 23 and is definedby a set of logical cells managed by an operator or a given serviceprovider. The set of cells corresponds to a geographical area. Theoperator or service provider can define one or more IAs to cover all thegeographical areas in which it provides a service.

Several IAs can cover all or part of the same geographical area, forexample if that area is covered by more than one operator or serviceprovider.

Interception of a given target subscriber in a given IA is initiated bya lawful enforcement agency (LEA). A lawful enforcement monitoringfacilities (LEMF) center 28 manages interception-related information(IRI) 29 delivered by the IMC 26 and intercepted data 210 delivered bythe IE 110 _(i).

A target subscriber is defined by an international mobile station ISDNnumber (MSISDN). The MSISDN to be intercepted and the addresses of theLEMF centers 28 to which that information must be sent are managed atthe level of the IMC 26. In the IMC, management of the interception isbased on an approach at the IA level, subject to the following rules:

a target subscriber can be intercepted in one or more IAs,

a radio control point (RCP) 211 can cover more than one IA, and

an IA can be covered by more than one RCP 211.

At the level of the interception equipment 110 _(i), the data concerningthe target subscribers is also organized at IA level. Accordingly, anIMC 26 delivers a list of the IAs to all the IE 110 _(l) through 110_(n) of a MSC 24 (name of each IA and information relating thereto).

When an interception has been defined:

the IMC 26 sends (at 212) the MSISDN of the target subscriber to the RCP211 concerned, i.e. the one associated with the IA, and

the IMC 26 transmits (at 213) the MSISDN of the target subscriber andthe identifier of the LEMF user of the LEA 27 to which the interceptioninformation must be sent to each IE 110 _(l) through 110 _(n) of the MSC24 concerned.

When a target subscriber receives or makes a call, the call is directedby the SSP 25 to the PCM loop 16 before it is directed to its finaldestination 14.

The interception equipment 110 _(i) performs the following operations inparticular:

it determines the IA concerned from the identifier of the cellsassociated with the intercepted call, or from the MSISDN number of theintercepted subscriber, if their location is unknown,

it extracts signaling information and voice data from the channelcorresponding to the intercepted call (identified by the interceptiondata 215 supplied by the RCP 211), and

if the call concerns a subscriber to be intercepted:

the interception equipment 110 _(i) performs the interception usinginterception data included in the signaling associated with the calland/or on a dedicated data channel incorporated into the loop 16 and/oradditional interception data received from the RCP 211,

the IE 110 _(i) sends (at 216) the interception related information tothe IMC 26, and

the IE 110 _(i) sets up one or two ISDN digital calls (at 210) to theLEMF 288 concerned.

If two calls are set up at 210, they respectively correspond to sendingand receiving. If only one call is set up, sending and receiving arecombined prior to transmission.

The IMC 26 transmits (at 29) interception reports to the LEMF 28. Afirst report is supplied at the beginning of each call intercepted and asecond report is transmitted at the end of the call. Each reportincludes an interception reference for cross-referencing to theinformation supplied (at 210) by the interception equipment.

The embodiment described above can easily be adapted to suit othercommunications systems without departing from the scope of theinvention.

The operation of the various units downstream of the interception loopare not described in detail. They are not directly relevant to theinvention and are described elsewhere, for example in the context ofstandardization.

What is claimed is:
 1. A method of intercepting a telephone call in atelecommunications system using at least one switch, characterized inthat signals in an interception loop in said switch and to which pulsecoded multiplex (PCM) containing the call to be intercepted has beendiverted are sampled at high impedance before they are directed to theaddressee.
 2. An interception method according to claim 1, characterizedin that the signal sampled at high impedance is directed to interceptionequipment which extracts said call to be intercepted from the PCM.
 3. Aninterception method according to claim 2, characterized in that saidinterception equipment is connected to an interception management centerfeeding one or more separate telephone tapping centers.
 4. Aninterception method according to claim 3, characterized in that each ofsaid telephone tapping centers correspond to a geographical interceptionarea such as a state or an administrative region.
 5. An interceptionmethod according to claim 4, characterized in that each of saidgeographical interception areas is defined by at least one of thefollowing: a list of identifiers of cells of a cellular network formingsaid geographical interception area, a list of dialing prefixesallocated to said geographical interception area, at least one item ofinformation, supplied by way of a signaling parameter, defining thegeographical interception area to which the call to be interceptedrelates, and at least one item of information, supplied by the switch,defining the geographical interception area to which the call to beintercepted relates.
 6. An interception method according to claim 1,characterized in that the signals in said interception loop comprisevoice data and signalling interception data.
 7. An interception methodaccording to claim 1, characterized in that the signals in saidinterception loop comprise only voice data, interception data concerningsaid call to be intercepted being transmitted to said interceptionequipment on a dedicated line by control means of the switch handlingsaid call to be intercepted.
 8. An interception method according toclaim 1, characterized in that the interception data of the call istransmitted in part together with the signals carried by saidinterception loop and in part via a dedicated line.
 9. An interceptionmethod according to claims 1, to 5, characterized in that saidinterception can cover a plurality of lines corresponding to the samesource and/or the same destination.
 10. An interception method accordingto claim 1, characterized in that said telecommunications system is oneof the following: an integrated services digital communication network,a cellular mobile radio network, or a satellite radio network. 11.Equipment for intercepting a telephone call, in a telecommunicationssystem using switch, characterized in that it comprises at least onehigh-impedance line sampling signals in an interception loop in saidswitch and to which the pulse coded multiplex (PCM) containing the callto be intercepted has been diverted before it is directed to theaddressee.
 12. Interception equipment according to claim 11,characterized in that it receives signalling data transmitted by acontrol center on a dedicated line and enabling extraction of the callto be intercepted.
 13. Interception equipment according to claim 11,characterized in that it comprises means for transmitting an interceptedcall to at least one telephone tapping center corresponding to separategeographical interception areas.
 14. A telephone call interceptionmethod for a switching network, comprising: providing an interceptiontarget identifier from an interception management center to a radiocontrol point and to interception equipment of a mobile switchingcenter; providing an indication of said interception target identifierfrom said radio control point to a service switching point of saidmobile switching center; diverting a call to a dedicated PCM loop insaid service switching point, when said call involves a stationindicated by said interception target identifier; sampling the PCM ofsaid diverted call at a high impedance sampling point of said dedicatedPCM loop to provide intercepted data to said interception equipment; andafter said sampling, directing said call through said switching networkto the destination station.
 15. The telephone call interception methodas set forth in claim 14, wherein: said interception management centerprovides a monitoring facility identifier to said interceptionequipment; and said interception equipment directs said intercepted datathrough said switching network to a monitoring facility in accordancewith said monitoring facility identifier.
 16. The telephone callinterception method as set forth in claim 15, wherein said interceptionmanagement center sends interception related information to saidmonitoring facility with cross-reference information indicating saidintercepted data provided by said information equipment.
 17. Thetelephone call interception method as set forth in claim 15, wherein:said interception management center provides more than one monitoringfacility identifier, for the same interception target identifier, tosaid interception equipment; and said interception equipment directssaid intercepted data through said switching network to more than onesaid monitoring facility in accordance with said more than onemonitoring facility identifier.
 18. The telephone call interceptionmethod as set forth in claim 17, wherein said monitoring facilities eachcorrespond to a geographical interception area.
 19. The telephone callinterception method as set forth in claim 18, wherein said geographicalinterception area is a state.
 20. The telephone call interception methodas set forth in claim 18, wherein said geographical interception area isan administrative region.
 21. The telephone call interception method asset forth in claim 18, wherein each said geographical interception areais defined by one or more of: a list of identifiers of cells of acellular network forming said geographical interception area, a list ofdialing prefixes allocated to said geographical interception area, atleast one item of information, supplied by way of a signallingparameter, defining the geographical interception area to which the callto be intercepted relates, and at least one item of information,supplied by the switch, defining the geographical interception area towhich the call to be intercepted relates.
 22. The telephone callinterception method as set forth in claim 14, wherein the signalsintercepted in said loop comprise voice data and signalling interceptiondata.
 23. The telephone call interception method as set forth in claim14, wherein: the signals intercepted in said interception loop consistof voice data, and interception data concerning said call is transmittedto said interception equipment on a dedicated line by control means ofsaid mobile switching center.
 24. The telephone call interception methodas set forth in claim 14, wherein said interception target identifierindicates a plurality of lines relating to and identical entity.
 25. Thetelephone call interception method as set forth in claim 14, whereinsaid switching network is an integrated services digital communicationnetwork.
 26. The telephone call interception method as set forth inclaim 14, wherein said switching network is a cellular mobile radionetwork.
 27. The telephone call interception method as set forth inclaim 14, wherein said switching network is a satellite radio network.28. An interception equipment for supporting telephone call interceptionin a switching network, comprising: a high-impedance line samplercoupled with a dedicated PCM loop to provide intercepted data, a switchof said switching network diverting a call to be intercepted to saidloop to obtain said intercepted; means for receiving a monitoringfacility identifier and; means for directing said intercepted datathrough said switching network to a monitoring facility indicated bysaid monitoring facility identifier.
 29. The interception equipment forsupporting telephone call interception as set forth in claim 28, furthercomprising means for receiving signalling data, over a dedicated line,said signalling data and enabling extraction of said intercepted data.